This invention relates generally to pumps and control systems therefor and more particularly to a power control systemt for multiple pumps of the variable volume type that are driven by a single engine with at least two of the pumps having the same capacity.
Although hydraulically powered vehicles utilizing hydraulic pumps to operate hydraulic actuators are widely used in construction and other types of machinery, the improvement of their control system is required because recently the number of hydraulic pumps has tended to increase.
Accordingly, the present invention provides a power control system with a high efficiency which is necessary for controlling multiple pumps of the variable volume type that are driven by a single engine.
The reason for this will now be explained hereunder. Considering a case where three pumps are involved, for an example: even though the tilt control is combined with known circuitry, it is made necessary to change the pilot portion of the tilt control in FIG. 8a to the one having a stepped plunger as shown in FIG. 8b, providing two pilot ports thereto and feeding the output pressure of other pumps respectively to said pilot ports. Therefore, the steps of pilot plunger and, accordingly, the number of pilot ports must be increased as the number of pumps increases, resulting in the disadvantages that the structure of tilt control becomes complex and the number of man-hours for plumbing increases thereby.
Further, this control system using a multi-stepped pilot plunger basically works satisfactorily with all pumps operated under loaded condition, but limits the usable power for operating pumps at a lower power than the maximum power of an engine when any other pump is under a no load condition.
In other words, there is a drawback in that, as any pump operating at constant power puts out higher pressure, the usable power for other pumps is reduced.